Constraints-based traffic engineering involves traffic routing in a network where routing or path computation decisions are made to determine whether certain constraints are satisfied for a path. Constraints can include administrative policies, quality of service (QoS) requirements (that relate to performance requirements, load balancing, and scalability factors), network resource availability, and so on. QoS constraints include total path delay, available bandwidth, loss rate, hop count, and any other user defined costs. These constraints-based routing mechanisms include policy routing (where the constraints are administrative policies) and QoS routing (involving QoS constraints). There are two categories of constraints-based problems: constraint satisfaction problem (CSP) and constraint optimization problem (COP). A CSP continues to look for solutions until one solution is found that satisfies all the specified constraints. A COP continues to look for all possible solutions or all possible solutions found until a pre-configured time period has expired, and then determines the “best” solution based on an optimization criterion or criteria.
There are two broad categories of routing: intra-domain routing and inter-domain routing. Current inter-domain routing protocols, such as the border gateway protocol (BGP), are based on the shortest path from the source to destination as well as on policy-based preference or other configuration values. As for intra-domain routing, currently most QoS requirements are handled by traffic engineering (TE) approaches via manual configuration or the multiple protocol label switching (MPLS) switching technologies. A path satisfying the required QoS constraints can be set up using protocols such as the resource reservation protocol (RSVP). Then, routing is explicitly carried out via switching technologies such as MPLS.
A constraints-based routing computation technique that can rely on distributed local path solution computations has greater flexibility and scalability.